What Are Powder Cores? FeNi, Sendust and MPP Explained
Powder cores are magnetic cores made from insulated metal alloy powder pressed with a distributed air gap, giving stable inductance under DC bias. FeNi (iron nickel) offers the highest saturation (Bs ≥1.5T) for high-current power; Sendust balances cost and loss; MPP delivers the lowest core loss among metal powders. Choose by current, frequency and loss budget.
If you have opened a power inductor, you have probably seen a gray or brown toroid made of compressed metal powder. These are powder cores, and they are the quiet workhorses of DC-DC converters, PFC stages and EMI filters. Here is what they are and how to tell the main types apart.
What is a powder core?
A powder core starts as a metal alloy powder. Each particle is coated with an insulating layer, mixed with a binder, and pressed into a core shape. The insulation between particles creates a distributed air gap throughout the magnetic path, unlike ferrite or silicon steel cores that need a physical air gap.
Why the distributed air gap matters
- Inductance stays stable under high DC bias (no sudden saturation knee)
- Magnetic flux is distributed, so stray EMI from gap fringing is reduced
- Core loss can be tuned across a wide frequency range by material choice
FeNi (iron nickel) powder cores
FeNi (50%Fe-50%Ni) is the high-performance option: saturation flux density Bs ≥1.5T, permeability range about 14–160, and stable behavior from −40°C to +180°C. It is the material of choice for high-current inductors in AI GPU VRM, EV chargers and server power where ferrite would saturate or grow too large.
Sendust (Kool Mu) powder cores
Sendust is an iron-silicon-aluminum alloy with saturation around 1.05T and very low magnetostriction noise. It offers a good balance of cost and core loss for PFC inductors, buck converters and EMI filters in the 20kHz–1MHz range.
MPP (molybdenum permalloy) powder cores
MPP has the lowest core loss among common metal powder cores and a stable temperature coefficient, making it ideal for precision filters, high-Q resonant circuits and applications with tight inductance tolerance. Its saturation is lower (about 0.75T), so size grows at high current.
| Material | Saturation Bs | Typical μ range | Best for |
|---|---|---|---|
| FeNi (Iron Nickel) | ≥1.5T | 14–160 | High-current power, AI GPU VRM, EV |
| Sendust | ~1.05T | 26–125 | PFC, buck converters, EMI filters |
| MPP | ~0.75T | 14–550 | Precision filters, resonant circuits |
How to choose
- High DC current, tight size → FeNi
- Balanced cost and loss → Sendust
- Lowest loss and tight tolerance → MPP
- Very high frequency (>500kHz), low power → ferrite still wins on cost
YUTE Magnetics manufactures FeNi powder cores and custom inductors for power electronics. Contact us for a free material selection review with loss and temperature data.
Frequently Asked Questions
What is a powder core?
A powder core is a magnetic core pressed from insulated metal alloy particles. The insulation between particles creates a distributed air gap through the magnetic path, so inductance declines gradually under DC bias instead of dropping sharply at a saturation point.
Why are powder cores used in power inductors?
They combine high saturation with a soft inductance roll-off under load, and they avoid the fringing flux that a discrete machined gap produces. That makes them well suited to inductors carrying substantial DC current.
What is the difference between FeNi, Sendust and MPP powder cores?
FeNi (iron nickel) has the highest saturation at Bs ≥1.5 T for high-current power inductors. Sendust balances cost and core loss for PFC and EMI filter roles. MPP has the lowest core loss among metal powders and is used for precision filters and resonant circuits.
Do powder cores saturate?
They do have a saturation limit, but because the air gap is distributed throughout the material the inductance falls gradually as bias increases rather than collapsing at a threshold. That behaviour is easier to design around than a sharp saturation knee.
When should I use a powder core instead of ferrite?
Use a powder core when the inductor carries significant DC current and must hold inductance under bias, or when core size is constrained. Ferrite remains the better choice for low-power high-frequency conversion and for transformer functions.
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